1. Field of the Invention
Aspects of the present invention generally relate to a dual transmission stream generating device and method for generating a dual transmission stream which includes a normal stream and a turbo stream for digital broadcasting. More particularly, aspects of the present invention relate to a dual transmission stream generating device and method for improving a digital broadcast performance by generating a dual transmission stream which includes a normal stream and a robust-processed turbo stream in order to enhance a reception performance of an Advanced Television Systems Committee (ATSC) Vestigial Sideband Modulation (VSB) system which is a. terrestrial Digital Television (DTV) system.
2. Description of the Related Art
A single-carrier ATSC VSB system, which is a terrestrial digital broadcasting system used in the United States of America and in other areas, uses a field sync having 312 segments or packets. Hence, its reception performance is not good in a poor channel environment, especially, in a Doppler fading channel.
FIG. 1 is a block diagram of a transmitter and a receiver representing a general terrestrial digital broadcasting system that conforms to the ATSC DTV standard. The digital broadcasting transmitter of FIG. 1 is an Enhanced Vestigial Sideband Modulation (EVSB) system suggested by Philips, and is structured to generate and transmit a dual stream by adding a robust data to a conventional normal stream of the conventional ATSC VSB system.
As shown in FIG. 1, the digital broadcasting transmitter executes an error correction coding by induding a randomizer 11 to randomize the dual stream, a Reed-Solomon (RS) encoder 12 which is a concatenated coder to add a parity byte to the transmission stream to correct errors occurring during the transmission due to certain channel characteristics, an interleaver 13 to interleave an RS-encoded data in a certain pattern, and a trellis encoder 14 to map to 8-level symbols by trellis-encoding the interleaved data at a ⅔ rate.
The digital broadcasting transmitter further includes a multiplexer 15 to insert field syncs and segment syncs to the data which went through the error correction coding, as shown in FIG. 2, and a modulator 16 to insert a pilot tone by adding a certain DC value to the data symbols having the inserted segment sync and field sync, to perform the VSB modulation through pulse shaping, to up-convert to an RF channel band signal, and to transmit the converted signal.
Accordingly, the digital broadcasting transmitter multiplexes (not shown) and applies the normal data and the robust data to the randomizer 11 according to the dual stream scheme which transmits the normal data and the robust data in one channel. As shown in FIG. 1, the input data is randomized in the randomizer 11, the randomized data is outer-encoded in the RS encoder 12 which is an outer encoder, and the outer-encoded data is interleaved in the interleaver 13. The interleaved data is inner-encoded by 12 symbols at the trellis encoder 14 and mapped to 8-level symbols. The field sync and the segment sync are inserted to the mapped data in the multiplexer 15. Next, the multiplexed data is transmitted after the pilot tone is inserted, the VSB modulation is performed, and the multiplexed data is converted into an RF signal in the modulator 16.
A digital broadcasting receiver of FIG. 1, includes a tuner (not shown) to convert the RF signal, which is received through a channel, to a baseband signal, a demodulator 21 to perform sync detection and demodulation on the converted baseband signal, an equalizer 22 to compensate for a channel distortion occurring due to multiple paths with respect to the demodulated signal, a viterbi decoder 23 to correct errors in the equalized signal and to decode the equalized signal into symbol data, a deinterleaver 24 to deinterleave the decoded data which was interleaved by the interleaver 13 of the digital broadcasting transmitter, an RS decoder 25 to correct errors, and a derandomizer 26 to derandomize the data corrected at the RS decoder 25 and to output an MPEG-2 transmission stream.
Hence, the digital broadcasting receiver of FIG. 1 recovers the original signal by down-converting the RF signal to the baseband signal, demodulating and equalizing the down-converted signal, and carrying out channel decoding in an operation that is an inverse of the operation performed the digital broadcasting transmitter.
FIG. 2 shows a VSB data frame having the inserted segment sync and field sync of a digital broadcasting (8-VSB) system used, for example, in the U.S. As shown in FIG. 2, one frame consists of 2 fields, and one of the fields consist of a field sync segment, which is the first segment, and another of the fields consist of 312 data segments or packets. In the VSB data frame shown in FIG. 2, each of the data segments corresponds to one MPEG-2 packet and such segments consist of a 4-symbol segment sync and 828 data symbols.
In FIG. 2, the segment sync and the field sync, which are the sync signals, are used for synchronization and equalization in the digital broadcasting receiver. In other words, the field sync and the segment sync are already known to the digital broadcasting transmitter and the digital broadcasting receiver and are used as reference signals by the digital broadcasting receiver to synchronize and equalize the VSB data frame.
The terrestrial digital broadcasting system of FIG. 1 is structured to generate and transmit the dual stream by adding the robust data to the normal data of the conventional ATSC VSB system so that the robust data can be transmitted together with the normal data.
However, the terrestrial digital broadcasting system of FIG. 1 cannot enhance the poor reception performance of the conventional dual stream in a multipath channel even when the conventional dual stream is transmitted with the added robust data. That is, the reception performance is not improved at all even with the improved dual stream. In addition, with respect to the robust data (turbo stream), the reception performance does not show great improvement in the multipath channel or environment. Therefore, there is demand for generation of a dual transmission stream to effectively transmit the robust data (turbo stream) and the normal data (normal stream) and process the robust data (turbo stream) more robustly.